All nuclear power plants have some form of emergency core cooling system (ECCS) in the event that normal operation is lost and a major break occurs in the reactor cooling system. There are two phases to most ECCS—The injection phase when the pumps suction water from a large tank and pump that water into the reactor cooling system or reactor, and the recirculation phase when the pumps take water from the containment sump after all of the water has been pumped into the containment.
An ECCS has one major function and that is to provide makeup water to cool the reactor in the event of a loss of coolant from the reactor cooling system. This cooling is needed to remove the decay heat still in the reactor's fuel after the reactor is shutdown. ECCS in some plants may have a second major function and that is to provide chemicals to the reactor and reactor cooling system to ensure the reactor does not produce power.
The major components of an ECCS are water supplies (tanks), pumps, interconnecting piping, high pressure pumps, low pressure pumps, water storage tanks, accumulators, and a containment sump used to circulate the water through the reactor once the storage tanks are empty.
In a nuclear reactor, a suction strainer is located in the containment area and its purpose is to keep loose materials and debris, such as insulation, from getting to the suction of the ECCS pumps during the recirculation phase. The pumps perform an important and vital function at nuclear power plants. Again, a purpose of the strainers is to protect the downstream components, such as pumps and nuclear fuel assemblies, from being adversely affected by such debris. Suction strainers, by their nature, have a tendency to build up debris layers. In use, as water is circulated through the strainer, solid debris builds on the outer surfaces of the strainer. The recirculation continues until the ECCS is no longer needed in cold shutdown.
Structural considerations, hydrodynamic loading, and space constraints limit the size and shape of suction strainers in nuclear containment buildings.
One existing suction strainer design utilizes nested tubes which are produced from a perforated metal sheet. Ends of the sheet are butted together and welded to form a tube. In the nuclear power industry welding is highly regulated. It is, therefore, advantageous to reduce or eliminate welding in any nuclear application.
The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior strainers of this type. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.